Such sound-insulating interior linings increase the wellbeing of passengers traveling in the cabin of a transport means. In particular, cabins of commercial aircraft are exposed to a number of loud external noise sources, for example engine noise and noise of turbulent boundary-layer flow. The acoustic insulation of aircraft cabins using passive measures is confronted by new challenges as a result of the introduction of aircraft fuselages constructed from carbon-fibre reinforced plastic (CRP), because such fuselages, due to their lighter specific weight and greater rigidity, when compared to metal structures, are clearly more transparent to engine noise, in particular in the low-frequency range.
The essential requirements of acoustic insulation of aircraft cabins are: light weight; small volume; a high degree of sound insulation across the frequency range of the exciting sound sources; simple installation; simple production; low cost; and as far as possible the avoidance of using additional components. Up to now these requirements were met by standard cabin fittings and fitments which were modified with targeted passive measures to improve the acoustic characteristics. Such passive measures comprise, for example, the local reinforcement of glass wool insulation; the arrangement of open prepreg grids on the rear of cabin lining elements; the sealing of slits between lining elements; the elastic suspension of cabin fittings and fitments or cabin modules, for example crew rest compartments; and additional mass applied in a sheet-like manner.
Cabin fittings and fitments are widely produced in sandwich construction, comprising a honeycomb core and cover layers that are arranged on both sides of it, as is, for example, shown in DE 3720371. From more recent developments of cabin fittings and fitments, further-reaching and mass-neutral modifications of the sandwich construction are known, which modifications provide, for example, for the slitting of honeycomb cores in order to reduce sound radiation. However, mass-neutral measures share a common characteristic in that in the lower frequency range of the interfering sound sources only very slight improvements in the extent of the sound-insulation may be achieved.
An additional option to achieve reduced cabin noise levels consists of increasing the sound absorption. To this effect, prior art proposes, for example, the arrangement of microperforated absorption elements or absorbers in the form of small holes in the cover layer of cabin panels produced in sandwich construction, which with the enclosed air volume form a resonant system.